GB1588463A - Plastic aerosol containers and process for preparing same - Google Patents

Description

(54) PLASTIC AEROSOL CONTAINERS AND PROCESS FOR PREPARING SAME (71) We, UNION CARBIDE CORPORATION, a corporation organized and existing under the laws of the State of New York, United States of America, whose registered office is, 270 Park Avenue, New York, State of New York 10017, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to polyethylene aerosol containers and a process for preparing the same.

The present invention relates in general to a process which improves the hoop strength and the resistance of high density polyethylene containers to solvation by a variety of fluids such as hydrocarbons, oils, halohydrocarbon aerosol propellants and the like, with a consequent decrease in permeability toward these substances and other materials commonly confined under pressure in the improved containers. More particularly, the invention relates to relatively thin-walled high-density polyethylene containers which have been cross-linked and surface treated by fluorination to render them suitable for aerosol packaging using high pressure propellants.

In aerosol packaging, in which a product is dispensed by a propellant contained in the aerosol container, it is frequently desirable that the product be forced at a rapid rate through a nozzle orifice small enough to produce a fine mist. This is particularly the case with hair sprays, deoderants, furniture waxes and the like in which a small quantity of product is to be applied uniformly to an area in a few seconds of time. Accordingly, it is important that the propellant be contained in the aerosol package under a substantial pressure, sometimes even higher than 105 psig at 1300F, and as a corollary that the container itself be capable of retaining a high percentage of the propellant under the conditions commonly encountered in shipping, storage and usage of the packaged product.

These imposed conditions have heretofore favored metal as the principal construction material for aerosol containers, and in fact. the overwhelming majority of such containers in commerce to date are formed from conventional tin plate stock. While metal aerosol containers have ample strength, even with thin walls, to contain the substantial internal pressure created by the propellant, there are a number of disadvantages in the use of metal which could be obviated if a suitable plastic construction material were available. Among the principal disadvantages are the tendency to rust and produce rust stains on shelves, clothing, etc., a low resistance to permanent shape deformation, i.e., denting, during shipping and handling, and the lack of versatility in container configuration using practical and economical forming methods.Also in cases where glass or metal aerosol containers become severely overheated and explode, the shrapnel produced can be highly injurious.

In view of strength and permeability problems involved in aerosol containers, it is not surprising that the bulk of the extensive literature on the subject of organic plastics for this use have been concerned with the so-called engineering resins. Such resins have high tensile strength, high tensile modulus and high creep resistance, and include nylon, polyacetals, polybutylene terephthalate. melamine and nitrile resins. Engineeringrresins are expensive on a cost per container basis due to the required wall thickness and hence a large amount of relatively expensive resin must be employed. Moreover. in some cases such as nylons and acetals, there is a high permeability to water. The melamines are difficult to mold and also exhibit high moisture permeability.Poor solvent resistance. especially to ethanol, brittleness and creep problems are the principal disadvantages of the nitrile resins. Also, the thermoplastic polyester resins have poor alkali resistance and poor compatibility with .methylene chloride.

Polyolefins, on the other hand, particularly polyethylenes and polypropylenes, not being distinguished by outstanding strength properties, have generally been considered as unsuitable for high pressure aerosol container construction, although such containers for low pressure formulations have been suggested. Also it has been proposed to coat the internal surface of a polyethylene container with a relatively impermeable polymer such as an acrylate to partially overcome the difficulties caused by the high permeability of the polyethylene substrate. The coating process, however, tends to leave pinholes in the barrier coating, and disposal of the solvent from the coating solution can create a variety of additional problems.

Without specific reference to high pressure aerosol containers, polyethylene and polypropylene articles such as films and the like have beèn subject to a wide variety of treatments which either chemically or physically affect their permeability, hardness, solubility, surface energy or surface tension and printability. We have found however, that the properties of a polyolefin resin essential to the formation of a commercially practical high pressure aerosol container can only be attained by the proper selection of the starting polymer coupled with a modification procedure in which a number of factors are critical and apparently interrelated in a manner not yet fully understood.

In accordance with the present invention, there is provided a polyethylene enclosure member suitable for use in a high pressure aerosol dispensing system wherein the enclosure member may contain the fluid propellant either- alone or in addition to the material to be aerosolized, the polyethylene having a melt index (as measured by ASTM test No. D-1238) of zero, a density of at least 0.94, preferably at'least 0.95, grams/cc, and a gel content of from 50, and preferably from' 70, to 99.5 weight percent, at least the internal wall surface of the enclosure being fluorinated to contain from 0.5 to 100 micrograms, preferably 1 to 50 micrograms, fluorine per square centimeter.

As used herein, the term gel content in percent is defined as 100 times the weight of polyethylene insoluble in refluxing xylene at atmospheric pressure divided by the weight of the polyethylene mass initially placed in contact with the refluxing xylene. A typical procedure used to determine the gel content is essentially as et forth in Kang, et awl., J. Am.

Chem. Soc. 89, 1981(1967), and is as follows: A weighted sample of convenient size and held in a stainless-steel basket is immersed in xylene boiling under a pressure of 1 atmosphere (absolute). 0.5 to 1.0 weight percent of 2,6-di-t-butyl-p-cresol is added to the xylene as an antioxidànt, as a further insurance against oxidation.of the polyethylene, a nitrogen atmosphere over the apparatus is used. The sample is periodically, typically at 18 to 24 hour intervals, removed from the xylene, dried under vacuum for 12 two 18 hours, weighed and again extracted, dried and wéighed until constant weight is attained.

The configurationof the enclosure member is not'a critical factor,' but usually it is- tubul.ar in nature with the closure at one end being integral with the side walls and composed of the same modified high density polyethylene. The close at the other end is any of, the conventional valve and nozzle devices commonly used in metal high-pressure aerosol dispensers, and is not a part of the present invention.Although the tubular shape of the enclosure member need not be cy!indrical, i.e. the longitudinal walls can bulge inwardly or outwardly, or both, and contain cameo and intaglio decoration and/or printing, an essentially cylindrical or spherical shape is a preferred configuration from the standpoint of ease of formation and efficient use of the polyethylene construction material. Preferably the ratio of diameter to wall thickness in simple cylindrical shapes is within the range of 18:1 to 7.6:1, and more preferably within the range of 12:1 to 7-.6:1, with wall thicknesses being at least 0.013 inch. In containers having diameters of the order of 3 inches, the wall thickness can exceed 0.45 inches.

In a cylinder whose walls are thin relative to its diameter, the initial hoop stress, S, is determined by the equation:

wherein "P" is the net internal pressure in the cylinder in pounds per square inch, "D" is the outside diameter of the cylinder in inches, and "t" is the wall thickness in inches. Using this criterion, the modified high density polyethylene used in the construction of the present aerosol containers is, when in a cylindrical configuration having a wall thickness of 0.128 1 .007 and an outside diameter of about 1.65 inches, capable of withstanding an initial hoop stress of 500 pounds per square inch for thirty days at 1300F. while containing a mixture of fluorotrichlotomethane and difluorodichloromethane in equal parts by weight.Moreover, the said enclosure member will not rupture and neither will it lose more than ten per cent of its contents through permeation loss.

The enclosure member is formed from polyethylene having a density of at least 0.94 and preferably of at least 0.950 grams per cubic centimeter by any of the methods well known in the art. These include blow molding, injection blow molding, rotomolding, injection molding and the like provided only that the forming method chosen does not unduly degrade the starting resin and unduly alter its essential properties. The starting resin can also contain colorants, antixodants, fillers and the like of the kinds in the proportions which do not adversely affect the strength or permeation properties of the enclosure member.

Since the gel content of the starting high density polyethylene is usually substantially below 5 percent and since we have found it to be essential that the gel content of the polyethylene of the enclosure member must be at least 50 percent, it is necessary to crosslink the resin either during or after the forming operation to attain the aforesaid minimum gel content.

The upper limit of the gel content is found to be not as critical as the lower limit, and accordingly a gel content range of 70 to 99.5 percent is suitably imparted, preferably 80 to 95 percent. The crosslinking can be accomplished either by means of chemical agents or irradiation in accordance with methods well known in the art. It is necessary from our observations that the crosslinking be carried out sufficiently to reduce the melt index of the resin in the walls of the enclosure member to zero, independent of the particular radiation dose used or the particular method of crosslinking employed.

In the chemical method, crosslinking can be accomplished by mixing a free radical generating substance into the starting polyethylene and heating the mixture to effectuate the desired reaction. A variety of free radical generating materials are commercially available, of which the most common is dicumyl peroxide. Since the polyethylene that is crosslinked to the degree necessary to obtain the required gel content for the present invention is, as a practical matter. no longer formable by thermal means, the heating to cause crosslinking is often but not necessarily, the same heating used to form the enclosure member. For instance, high density polyethylene compositions are commercially available for use in rotomolding which contain premixed quantities of crosslinking agents.In the forming and crosslinking combined operation the composition is placed in a hollow metal mold and the mold is rotated and tumbled to uniformly spread the powder over the inside surface, while the mold is heated in an oven at 600" to 6500F for 10-15 minutes. The composition melts, flows, and crosslinks simultaneously to produce upon cooling a crosslinked article conforming to the mold internal configuration Alternatively, a preformed enclosure member can be molded of the starting resin in conventional manner and thereafter immersed in a crosslinking agent such as dicumyl peroxide for a period sufficient to allow diffusion thereof into the molded form to the required degree. Thereafter the enclosure member, properly supported to avoid collapse can be heated briefly to activate the crosslinking reaction.The required proportions of crosslinking agent and resin and the precise operating conditions can routinely be determined in each case to produce the required degree of crosslinking in terms of the gel content of the resin.

The preferred crosslinking technique is irradiation of the preformed enclosure member with high energy ionizing radiation having an energy equivalent of from 25,000 to 10,000.000 volts and a dosage of from 0.5 to 100 mega rads. Preferably the irradiation dosage is from 5 to 50 mega rads. Irradiation of the enclosure member can be accomplished in the known manner using a Van de Graaf generator, a resonant transformer or a source of gamma rays such as cobalt 60 or cesium 137. Other suitable irradiation techniques are set forth in U.S. Patent 2,897,092.

Although from our investigation and the data set forth in the examples appearing hereinafter it is apparent that the gel content of the polyethylene is a critical factor, it is not apparent in what precise manner the gel content is related to the other aspects of the treating procedure necessarily employed in the practice of this invention. It is possible that the surface treatment with fluorine. which apparently involves a very complex reaction mechanism. is a significant factor. but this relationship has not been proven.Although polyethylenes have heretofore been irradiated in order to increase the rate of subsequent halogenation. there has been, to our knowledge. no previous investigation of the effects of combined irradiation and fluorination on the capacity of a polyethylene enclosure member to retain high-pressure aerosol propellants such as CF2Cl2 and CFCl. This is not particularly surprising since the process of polymer creep and consequent distortion or rupture in such aerosol enclosures occur ordinarily over a relatively long period of time.

Accordingly. relationships between seemingly unrelated factors are not noticed except by investigators whose particular interest is in plastic high pressure aerosol containers.

The essential fluorination treatment of the present invention can be carried out either prior to or subsequent to the crosslinking by irradiation or chemical means. The precise technique employed is not a critical factor provided that at least the internal surface of the enclosure is contacted with fluorine or a fluorine precursor in sufficient amount and for sufficient time to impart from 0.5 to 100, most preferably 5 to 25, micrograms per square centimeter of fluorine to that surface. If desired, the external surface can also be fluorinated with some beneficial results, but the necessary strength properties of the enclosure members are not achieved by fluorinating only the external surface.

Accordingly, the modification treatment of the present invention whereby polyethylene enclosures suitable for use as high pressure aerosol containers are prepared, comprises forming an enclosure member from a high density polyethylene having a density of at least 0.94, and preferably of at least 0.95, gram/cc., a melt index of 0.01 to 20 and a gel content of less than 50 weight percent, crosslinking the molecules thereof to increase the gel content to at least 50 weight %, preferably to within the range of 70 to 99.5, and more preferably 80 to 95, weight percent, and to decrease the melt index to zero, and fluorinating at least the internal surface of the said enclosure member to impart from 0.5 to 100 micrograms per square centimeter of fluroine to that surface.

The following examples will illustrate the various modes of practising the present invention.

Example 1 Using a conventional blow molding technique, a large number of enclosure members were formed from polyethylene having a density of 0.953 and a melt inex of 0.1 and.a gel content of less than 1 percent. All of the- enclosures were cylindrical in shape with the bottom closure integral with and generally at right angles to the sidewalls. The opening at the top was formed with a 20 mm. neck adapted to form a tight-fitting closure with a conventional 20 mm. aerosol dispensing cap. The outside diameter of each cylindrical enclosure member was approximately 1.65 inches and the cylinder wall thickness was in the range of 0.12 to 0.135 inches. Forty-two of these enclosures were fluorinated by the following procedure. The enclosures were placed in a nickel-clad steel chamber, the walls of which were maintained at 600C.The door was closed and the chamber and contents were evacuated to approximately one torr. The chamber was then filled with a mixture of 25% (by volume) of commercial grade fluorine and 75% high purity nitrogen during approximately one minute. The chamber was filled to a final pressure of one atmosphere absolute (0 psig). The gas mixture was allowed to remain in contact with the enclosures for two minutes. The chamber was then evacuated to approximately one torr, refilled to one atmosphere with nitrogen evacuated a second time, refilled with nitrogen. the door opened and the enclosures were removed. The fluorination treatment imparted approximately 7 micrograms per square centimeter of each of the external and internal surfaces.Thirty of the fluorinated and 12 non-fluorinated enclosure members were irradiated by electrons from a Van de Graaff generator having an energy equivalent of 1.6 million volts to a dose of 20 megarads. The irradiation treatment raised the gel content of the polyethylene to 90-95 percent and lowered the melt index to zero. The enclosures, either irradiated or fluorinated or both according to the above-described procedure and others which received no treatment, were filled with approximately 100 grams of mixtures of halocarbon propellants, capped with convention 20 mm aerosol bottle caps and tested by exposure to various test temperatures for various times. Table 1 below sets forth the loss of weight of the containers.

In addition bulges, splits, cracks or other visible failure of the containers were recorded. In the table, i'Irr." and "F," denote that the pretreatment included irradiation and fluorination respectively. and "R.T." denotes ambient room temperature. i.e. about 70"F.

The propellant mixture sealed in the enclosures identified in Table I as "30/7012/11" consisted of 30 parts by weight difluorodichloromethane and 70 parts by weight of fluorotrichloromethane. The propellant mixture identified as 50/50; 12/all consisted of equal parts by weight of the aforesaid two halomethanes. The pressure values indicated in the Table in terms of psig are the pressures autogeneously generated by the aforesaid propellant mixtures at the temperatures indicated. The column heading "E D Mils" denotes the increase in diameter of the enclosures at their midsection over the test period indicated, in mils. In obtaning the test values reported. an average of the values for five test enclosures was made for those enclousres which were both irradiated and fluorinated. All other values are the average for two enclosure members unless otherwise specified. Test results indicated as "failed" are those in which the enclosure split or ruptured, releasing the contents; Tests at 1300F were discontinued after one month.

TABLE I Permeation and expansion testing of bottles subjected to complete, partial, or no treatment 13 Days 4 Weeks 3 Months Enclosure Temperature & Loss # D Loss # D Loss # D Treatment Propellant Pressure % Mils % Mils % Mils % Mils F2 & Irr. 30/70; 12/11 R.T. 23 psig 13 2 .06 6 .28 5 F2 Only .14 0 .07 2 .38 5 Irr. Only .2 21 1.3 31 7.9 24 No Treatment .3 29 2.2 30 11.2 27 F2 & Irr. 30/70; 12/11 100 F 46 psig .15 9 .31 14 1.39 17 F2 Only .17 12 .36 13 1.59 21 Irr. Only 2.5 39 8.4 46 31.6 43 No Treatment 3.4 43 11.1 47 42 46* F2 & Irr. 30/70; 12/11 130 F 76 psig .67 28 1.7 34 Discontinued F2 Only .51 28 Failed at Irr. Only 10.2 66 26 72 One No Treatment Failed Failed Month *One of two bottles failed between 8 and 12 wks.

TABLE I (Continued) Preparation and expansion testing of bottles subjected to complete, partial or no treatment 13 Days 4 Weeks 3 Months Test Wt. Wt. Wt.

Enclosure Temperature & Loss # D Loss # D Loss # D Treatment Propellant Pressure % Mils % Mils % Mils F2 & Irr. 50/50; 12/11 R.T. 38 psig .15 5 .09 6 .43 3 F2 Only .16 1 0.14 3 .63 5 Ir. Only .35 17 1.35 27 7.4 44 No Treatment .26 24 1.87 32 9.7 28 F2 & Irr. 50/50; 12/11 100 F 67 psig .14 15 .33 19 1.7 21 F2 Only .16 13 .34 15 1.9 19* Irr. Only 2.2 37 7.5 46 28.9 44 No Treatment 3.2 45 10.4 53 Failed 4-8 Wks.

F2 & Irr. 50/50; 12/11 130 F 105 psig .93 41 2.9 48 Discontinued F2 Only Failed Failed at Irr. Only 10.6 79 27 95 One No Treatment Failed Failed Month * One of two bottles failed between 8 and 12 weks.

The data in Table I, especially those concerning room temperature testing, show apparent slight decreases, weight gains or diameter decreases in some cases, These results reflect random experimental errors and are small in magnitude.

It is apparent from the data of Table I that the enclosures which were both crosslinked and fluorinated in accordance with the process of the present invention are able to withstand a hoop stress of about 625 psi at 1300F generated by typical halohydrocarbon propellants for a period of at least one month without undue weight loss and with relatively small distortion. Those enclosures which were given neither the fluorination nor the crosslinking treatment, and those given only the fluorination treatment failed completely under these severe conditions. Those which were crosslinked but nor fluorinated, while not rupturing under these conditions, nevertheless lost an undue amount of their propellant charge and were grossly distorted.

Example 2 (A) A number of cylindrical enclosures similar to those prepared in Example 1 were molded from a polyethylene resin having a melt index of 0.1 a density of 0.953, a gel content of < 1 percent, and containing 4 weight percent of a dark blue masterbatch pigment polyethylene resin. The enclosures had a lateral wall thickness of 90 to 100 mils and a capacity of about 3.8 fluid ounces. The enclosures were then exposed to a variety of irradiation and fluorination treatment conditions as part of a statistically designed experiment using the same general procedures as described in Example 1.The enclosures (now having a melt index of zero and a gel content greater than 50% by weight) were then filled with approximately 100 grams of a mixture of 30 parts by weight of CF2Cl2 and 70 parts by weight of CFCl3, tightly sealed and placed in an oven maintained at 1300F. The autogenous pressure in the enclosures under these conditions was approximately 76 psi.

After a period of one month in the oven, the loss of weight and the diametral expansion were determined. The results are set forth in Table II below.

TABLE II Permeation and expansion test results from treatment under varied conditions Process conditions F2 Treatment One Month, 130 F F2 Irrad. Order of Diametral Time Temp. Conc. Diluent Dose Treat- Weight Expansions Sample (Min) C Vol.% Gas Mrads ments Loss% Mils 1 1 40 25 He 25 F2 1st 2.7 17 2 2 40 50 He 15 F2 2nd 6.4 21 3 1 60 50 N2 25 F2 2nd 3.4 22 4 2 60 25 N2 15 F2 1st 1.7 18 5 2 60 25 He 25 F2 2nd 2.1 4 6 1 60 50 He 15 F2 1st 3.7 23 7 2 40 50 N2 25 F2 1st 4.8 23 8 1 40 25 N2 15 F2 2nd 2.1 18 It is apparent from the data in Table II that excellent results were obtained with these enclosures. The average permeation weight loss for the group is 3.4 percent, and the diametral expansion is so slight as to be virtually unnoticeable. The hoop stress under the test conditions was approximately 622 psig.It is also to be noted that the order in which the irradiation and the fluorination treatments were carried out is not a critical factor.

(B) To demonstrate that chlorine and fluorine are not equivalent surface treating materials in the process of this invention, six enclosures as used in Example 1 supra were chlorinated according to the following procedure: The enclosures were placed in a sealed chamber and the chamber evacuated to 3 torr, refilled with nitrogen to atmospheric pressure, again evacuated to 3 torr, again filled with nitrogen and finally evacuated to 3 torr. Chlorine gas was directed into the evacuated chamber in such a manner as to flow directly into the enclosures as well as the chamber generally. The chlorine was allowed to flow in to reach one atmosphere pressure over a period of 2.5 minutes, then continue to flow through the chamber to a caustic scrubber at approximately 5-10 cc per second for one hour.After one hour, the reactor was purged with N2 at 20 liters per minute (roughly 20 liter reactor) for 15 minutes. Bottle weight gain was 0.14 to 0.19 percent immediatly after reaction. These weight gains remained constant after overnight standing for five hours evacuation at less than three torr.

The enclosures were irradiated to a dosage of 20 megarads either not at all, before, or after chlorination. Three were analyzed for chlorine content by Neutron Activation Analysis. Chlorine content is recorded in Table III. There is no evidence for radiation acceleration of chlorination, and in fact, the greatest weight gains were noted on non-irradiated samples although the differences are perhaps not statistically significant. The three bottles not analyzed were filled with the same propellant as in part (A), capped and placed on test as noted in Table III, as were the other treated bottles. The data show that chlorination does not provide the same benefits that fluorination does, with or without irradiation.

Example 3 A series of enclosures identical to those of Example 2, part (A) except that the pigment was omitted, were treated with a mixture of 25 percent fluorine and 75 percent nitrogen for two minutes at 600F, washed with distilled water, dried in air and then irradiated to a dosage of 20 megarads to decrease the melt index to zero and increase the gel content to greater than 50% by weight. The enclosures were thereafter filled with a cologne formulation comprising alcohol and essential oils (perfume) and containing as a propellant a mixture of 10 weight percent CCl2F2 and 90 weight percent ClF2C-CClF2, capped with conventional 20 mm. aerosol dispensing caps and exposed to three different temperature conditions for a period of 28 days. The test data is set forth in Table IV below and show the superior performance of the enclosures. In particular, the data establish that the presence of such typical aerosolized product components as alcohol and perfume oils does not harm the bottle of this process. Especially, the presence of the alcohol does not raise the permeation rate to a high level or cause undue swelling or bulging of the' container.

TABLE III Elevated temperature permeation and diametral expansion testing companing fluorinated and chlorinated aerosol enclosures with or without irradiation, using 30/70 propellants 12/11 at 130 F Time tested and results 5 Days 2 Weeks 4 Weeks Sample Wt. Loss #D. Mils Wt. Loss #D, Mils Wt. Loss #D, Mils Treatment g. g. g.

Irr. then Cl2 3.4 74 13 83 31 83 (Cl content 0.13% by wt.) Cl2 then Irr. (Failed at less than (Cl content 5 days) -- -- -- -15% by wt.) Cl2 only 4.0 76 Failed before (Cl content 2 weeks 13 % by wt.) TABLE IV Permeation and expansion results from a twenty-eight day test of aerosolized cologne formulation in fluorinated and irradiated HDPE bottles Diametral % Weight Loss Expansion Mils Test Temperature & No. of Approx. Pressure Enclosures Average Range Average Range Room Temperature 10 0.020 0.00-0.03 5.9 4-11 (22 psig) 100 F (35 psig) 10 0.135 0.03-0.17 12.6 9-15 130 F (45 psig) 10 0.756 0.61-0.97 22 20-26 TABLE V Permetion and expansion testing of treated HDPE aerosol enclosures filles with consumer product formulations Test Conditions Test Results 2 Weeks 4 Weeks Sample Test Wt.Loss Wt.Loss No. Formulation Temp. F g.D Mils g. D Mils

1 10.3 wt.-% Antiperspirant R.T. 0.25 6 0.48 15 2 # 26.9 wt.-% CCl2F2 100 0.42 16 1.44 34 3 62.8 wt.-% CCl3F 130 2.50 43 6.73 62 4 60.0 wt.-% Deodorant R.T. 0.02 4 0.06 11 5 # 40.0 wt.% CCl2F2 100 0.09 8 0.39 23 6 130 0.69 27 1.79 40 7 96.7 wt.-% Shaving Cream R.T. 0.03 5 0.06 14 8 # 2.84 wt.-% Isobutane 100 0.06 5 0.15 14 9 .46 wt.-% Propane 130 0.21 18 0.47 27 During these tests, room temperature was approximately 75 F. Results for four bottles were averaged for each entry.

Example 4 This example shows results with typical consumer product formulations, demonstrating that the invention works well with actual products, one of which contained a hydrocarbon propellant. HDPE enclosures of the type used for Example 1 were treated and irradiated according to the general procedure of Example 1 to produce enclosures with a melt index of zero and a gel content greater than 50% by weight. All were fluorinated in the same batch, using 25% F2 in N2 for two minutes dwell time at one atmosphere in a 60"C chamber. The enclosures were then filled, capped and placed on test at the conditions shown in Table V.

Weight loss and diametral expansion were measured periodically and recorded. Results for each entry in Table V are the average of four samples.

Examination of the results shows generally excellent performance.

Example 5 To demonstrate the effect that gel content has upon the properties of the enclosure members of the present invention. a number of enclosures were blow molded and fluorinated in accordance with the procedure of example 1, supra, except that fluorination followed irradiation. The enclosures were cylindrical in shape, and had a wall thickness of between 118 and 135 mils. The melt index of the polyethylene starting material was 0.1, and the density 0.953 and the gel content was zero. The enclosures were irradiated to obtain different gel contents. After fluorination, the internal and external surfaces contained approximately 10 micrograms of fluorine per square centimeter. For testing, the containers were filled with equal parts by weight of fluorotrichloromethane and difluorodichloromethane.The tightly sealed enclosures were tested in a 1300F hot air oven for 30 days. The behavior of the various samples under the test conditions are presented in Table VI below.

In general, permeation results of bottles which did not rupture or crack were in the acceptable region (approximately four to five percent with a few samples as high as approximately eight percent).

TABLE VI Results of testing HDPE bottles of different gel contents at 1300F with equal parts by weight of CFCI? and CF2CI.

Entry No. Gel Content Test Results 1 0 Severe Distortion and Cracking. Two of four ruptured, less than two weeks.

2 5 Severe Distortion and Cracking. 1 of 2 ruptured between two and four weeks.

3 47 Distortion and Cracking. l or 2 ruptured between two and four weeks 4 54 Distorted 5 7 Distorted 6 73 Slightly Distorted 7 78 No Significant Distortion These results demonstrate that a minimum gel content of 50% is required to prevent gross cracking and rupture of the bottles. It is also apparent from the data. and from examination of the apperance of the bottles. that clearly superior performance is obtained above about 70cue gel content.

(B) Aerosol bottles were blow molded of Diamond Shamrock Co. Type K-123 polypropylene in the same shape and size as those used in Example 2. Average wall thickness were 100 to 110 mils. The bottles were irradiated then fluorinated in the same reaction as in part A of this example. Different radiation doses were used. The degree of fluorine incorporation was not measured, however by comparisdn of other fluorinations of polyethylene and polypropylene, the fluorine incorporation was estimated to be 10 to 30 11 g/cm2.

The bottles were filled (where possible) with the same propellant mixture as in part A.

Test results are recorded in Table VII.

TABLE VII Nominal Radiation Dose (Megarads) Gel Content Remarks 20 16% Failed - Ruptured After 10 minutes in 1300 oven 50 48% Split or Cracked while being Filled 100 49% Split while being Filled or Neck Snapped while Crimping These data demonstrate that irradiation and fluorination of polypropylene, which can produce some crosslinking (as evidenced by gel content) does not produce a functional aerosol bottle. The resin becomes quite brittle.

(C) A third set of polyethylene enclosures. of the type used in Example 2, but without any added blue pigment and with wall thicknesses of 0.080 to 0.100 inches were tested. The resin had a 0.954 density, a melt index of 0.3 and a gel content of less than 1 per cent. When irradiated to 10 megarads (sides) and 15 megarads (bottoms) to give 50-6() per cent gel in the sides, fluorinated with a mixture of 25ago fluorine and 75cue nitrogen for 2 minutes at 60"C. and tested at 1300F. with a 30/70 weight-C/c mixture of CF,Cl,/CFClX for one month.

the enclosures expanded over 13% and lost from 49 to 69 percent of their contents at an approximate hoop stress of 660 psi. In contrast, comparable enclosures irradiated with the same dose, but molded of a different resin. and thus having a gel content of 75 to 85%, performed substantially better as evidenced by their loss of as little as 12cue of their contents and showing about 8% distortion. Although these results would not be acceptable in all cases, and are somewhat adversely affected by minor irregularities in wall thickness. they are generally satisfactory.Further trials with this latter group of enclosures, irradiated to 20 megarads (approx. 90% gel content) gave still further improved results. with weight losses of 3 to 13% and expansions of only 2 to 3%'. Still further trials with this latter resin showed that enclosures formed therefrom performed well when irradiated to attain a gel content of approximately 75% and tested at hoop stresses of about 580 to 710 psi generated with fluorocarbon propellant at 1300F. for one month.

Example 6 (A) A generally cylindrical enclosure with a neck configuration designed to accept a standard 20 mm aerosol bottle closure is molded of HDPE (0.8 melt index, 0.96 density.

less than 5% gel content). The enclosure is capped. filled with 50/50 by weight CF2Cl2 and CFClh and tested at approximately 7()0 psi hoop stress (generally internally by propellant pressure) for one month at 13() F. The bottle fails by swelling, distortion, and loss of about 50cue of its contents.

(B) Another such bottle is impregnated with dicumyl peroxide by immersion in the peroxide at 70-80"C. until approiximately 2% by weight is picked up. The enclosure is maintained at that temperature for three more days to help equilibrate the peroxide concentration. The enclosure is then supported internally by a close fitting metal rod. and placed in a close fitting metal mold where it is heated to 1800C for 4 minutes. After cooling. the enclosure is removed from the mold, and heated in a vacuum oven for 3 days at less than 25 torr at approximately 90"C in order to remove peroxide decomposition products. The gel content is increased to approximately 80%. After cooling, the enclosure is fluorinated as in example 1, and capped. filled, and tested as in part A supra. The enclosure does not distort significantly and loses less than 10% of its contents by permeation during the one-month test period.

Claims (10)

WHAT WE CLAIM IS:

1. A polyethylene enclosure member suitable for use in an aerosol dispensing system, the polyethylene having a melt index of zero, a density of at least 0.94 grams/cc., and a gel content of from 50 to 99.5% by weight, at least the internal wall surface of the enclosure member being fluorinated to contain from 0.5 to 100 micrograms fluorine per square centimeter.

2. An enclosure member according to Claim 1 wherein the polyethylene has a gel content of 70 to 99.5% by weight.

3. An enclosure member according to Claim 1 or 2 wherein the internal wall surface contains from 1 to 50 micrograms fluorine per square centimeter.

4. An enclosure member according to Claim 3 wherein the internal wall surface contains from 5 to 25 micrograms fluorine per square centimeter.

5. An enclosure member according to Claim 1 substantially as described in any one of the Examples.

6. A process for preparing a polyethylene enclosure member suitable for use as an aerosol container which comprises forming an enclosure member from polyethylene having a density of at least 0.94 grams/cc., a melt index of 0.1 to 20, and a gel content of less than 50 weight per cent, crosslinking the molecules thereof to decrease the melt index to zero and to increase the gel content to 50 to 99.5% by weight, and fluorinating at least the internal surface of said enclosure to impart from 0.5 to 100 micrograms of fluorine per square centimeter of that surface.

7. A process according to Claim 6 wherein the polyethylene is crosslinked to create a gel content of from 70 to 99.5% by weight.

8. A process according to Claim 6 or 7 wherein the walls of the enclosure member is fluorinated to contain from 1 to 50 micrograms fluorine per square centimeter.

9. A process according to Claim 6 substantially as described in any one of the Examples.

10. A polyethylene enclosure member obtained by a process according to any one of Claims 6 to 9.